Electroforming assembly for producing complexly shaped articles



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mn. 0 T N E V w AGENT United States Patent Office 3,515,662 PatentedJune 2, 1970 U.S. Cl. 204--281 2 Claims ABSTRACT OF THE DISCLOSUREPerforations in the recessed area of a surface mold are provided toproduce smooth, even, relatively stressfree deposition on the recessedarea. Fusible illets may also be used to form rigid bridges over partsof the recessed area. A specific product is an integrally formed,rigidly supported, relatively stress-free, electroplated mirror.

INTRODUCTION This invention relates to surface molds for electroformingcomplexly shaped articles by deposition processes and to means forfacilitating deposition in recessed areas of these molds. In particular,this invention relates to molds for producing electroplated, opticallysmooth, mirror surfaces with integral toroidal supports therefor and tothe stress-free, integrally-Supported mirrors thus produced.

Formation of articles by deposition onto a form or surface mold is quitecommon. If the mold includes small depressions, indentations, etc.,generally referred to herein as recessed areas, it is often difficult toachieve uniform deposition in these recessed areas. There are a numberof possible causes for this. One example is premature deposition acrossthe recessed area which closes 01T the recessed area from furtherdeposition and results in little or no deposition taking place in therecessed area itself. The bridge of deposition material thus formed,since it is formed randomly and without a support surface, is generallynot strong enough to contribute to the strength of the article formed. Asecond problem is that if the deposition process involves the evolutionof a gas, the evolved gas collects in the recessed areas of the moldwithout being able to escape. This inhibits further deposition in theseareas by interfering with the availability of the depositing material tothe recessed areas. Fluid stagnation may also occur in that part of thedepositing material which is trapped in the recessed areas of the mold.Deposition in these areas may therefore also be limited by depletion ofthe depositing material in the recessed areas. Finally, if the recessedarea is located at the juncture of two distinct parts of the mold orarticle to be formed, where these two parts, when formed, are ultimatelyof different thicknesses or rigidity, the article formed includes asubstantial amount of inherent stress at this juncture. Such stress is aparticular problem where a high degree of precision is required in thearticle formed, such as large electroplated mirrors.

OBJECTS OF INVENTION With a view to these problems, it is a primaryobject of the present invention to provide a mold surface having arecessed area with a means for facilitating deposition in the recessedarea.

Another object of this invention is to provide a means wherebystress-free sheet-like articles may be formed with integral and rigidlyattached supporting members therefor.

Still another object of this invention is to provide means for formingcomplexly shaped articles by deposition processes.

One other object of this invention is to provide an electroplatedrelatively stress-free, mirror and a rigidly attached, circumferentiallydisposed, integrally formed, toroidal support therefor.

BRIEF SUMMARY `OF THE INVENTION These and other objects are met, inaccordance with one embodiment of the present invention, by a surfacemold, with recessed areas therein, having perforations in these recessedareas, and also having a fusible fillet occupying portions of the spacesurrounded by the recessed areas. In the prefered form of the presentinvention, integrally formed, toroidally supported, electroplatedmirrors are provided, using as the moldl surface, an optically smoothmandrel connected to a perforated, fusible, toroidal member,circumferentially disposed near the other edge of the mandrel, through aperforated mold surface which provides a continuous curved surface fromthe optically smooth mandrel to the toroidal member. In addition, afusible illet is disposed in portions of the recession at the junctureof the flat connecting surface and the toroidal member.

DETAILED DESCRIPTION OF THE INVENTION While the specification concludeswith claims particularly pointing out and distinctly claiming thesubject matter of the present invention, this invention may be betterundersood from the following description, taken in conjunction with thefollowing drawings, in which:

FIG. 1 depicts, in cross-section, an electroform for producingrelatively stress-free electroplated mirrors with integrally formed,toroidal supports;

FIG. 2 is a detailed cross-sectional view of a part of the electroformshown in FIG. l; and

FIG. 3 is cut-away View of a part of the electroplated mirror andintegrally formed support therefor formed using the device shown inFIGS. 1 and 2.

Refering more specilicaly to FIG. l, there is shown a metallic mandrel 1having an optically smooth surface 2 for electroplating large, concavemirror surfaces. In order to provide rigid, stress-free support for amirror electroplated an metallic mandrel 1, a fusible perforated,toroidal member 3 circumferentially disposed around the edge of themandrel 1 is provided along with a gutter member 4 which abuts both themetallic mandrel 1 and toroidal member 3 and on which a connectingsurface between the deposit on the mandrel 1 and toroidal member 3 isformed. These elements are seen in more detail in FIG. 2.

In order to provide an even, smooth, rigid, deposit in the recessed areaformed by the metallic mandrel 1, the

ltoroidal member 3 and the gutter member 4, perforations 5 are providedat intervals in the recessed area. These are shown in FIG. 2, as is afusible fillet 6 located at the very tip of the recessed area. Otherfeatures include additional perforations 7 in the toroidal member 3, andan electrode extension 8 for providing relatively well distributedelectrical stress in the enclosed and recessed areas of the electroform.The electroplate 9 formed on this mold is also shown in FIG. 2, as is ashield 10 over the outer surface of the gutter member 4 and a bolt 11,which secures the gutter member 4 to the toroidal member 3. Since themember 3 is toroidal, the electroplate 9 is a double-walled hollowstructure, with the plating inside the perforations 5 forming tubularconnections between the two walls which form the double wall. Theextension 12 of form 3, which joins tangently the circular cross sectionof form 3, provides continuity with the gutter member 4.

In FIG. 3, the electroplate is shown after it has been re.- moved fromthe electroform shown in FIGS. 1 and 2, and

after the fusible, perforated, toroidal member and the fusible llet havebeen melted out.

While it has been found, in accordance with the present invention, thatthe perforations S are necessary to permit escape of evolved gases andcirculation of electrolyte material through the recessed area, theremaining perforations 7 in the toroidal member 3 serve a usefulfunction also. In particular, these additional perforations reduce theweight of the overall structure. Notwithstanding this, the structure issupported by the optimum shape, namely a torus. Further, the support isrigid but the structure is free of stresses caused by the mating ofseparate members, and particularly those induced by mating of separatemembers formed of dissimilar materials. Finally, and most importantly,stress induced by uneven plating on a complex shape is avoided.

While it is clear that this concept may be used to form, in a singlestep, a stress-free toroidally supported electroplated mirror, using forexample nickel or aluminum electroplating baths, it is equally clearthat the concept may be useful in a variety of other applications inwhich articles having complex shapes are formed by deposition processesonto a mold surface, particularly one having recessed areas. Gooddeposition within the recessed areas is facilitated by the presentinvention and rigid bridge supports across the recess area may beprovided to enhance the quality of the final article.

While the present invention has been described with reference toparticular embodiments thereof for purposes of clarity and convenience,it should be understood that numerous modifications may be made by thoseskilled in the art without departing from the inventions true spirit andscope. Therefore the appended claims are intended to cover all suchequivalent variations as come Within the true spirit and scope of thepresent invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electroforrning assembly for producing by electrodepositionthereon from a solution a double-walled hollow structure 9 of firstmetal having tubular connections between the two walls which are thedouble wall, including a form which is constructed of a second metalfusible at a relatively low temperature below the softening temperatureof the first metal;

is hollow, and substantially of the shape of the article to be formed;

is provided with apertures 7 in its wall for enery of solution into itshollow interior;

is provided with an electrode extension 8 in its hollow interior whichelectrode has a portion thereof extending through said Wall to theoutside of the form.

2. An assembly as claimed in claim 1 in which said form is substantiallycircular in cross section and has an addition an external extension 12,of the said second metal, which is joined tangently to the part ofcircular cross section.

References Cited UNITED STATES PATENTS 2,425,022 8/1947 Bart 204-192,024,521 12/ 1935 Harrison 204-9 2,425,022 8/1947 Bart 204-19 3,091,5785/1963 Hetherington 204l9 3,378,469 4/1968 .lochim 204-7 JOHN H. MACK,Primary Examiner T. TUFARIELLO, Assistant Examiner Us. ci. XR.

PO-Uw UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent No.3, 515, 662 Dated June 2, 1970 Invented@ Ference J. Schmidt It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 1l, change "euery" to entry line 17, change "an" to inammi-.xn SEALED SEP bm SEPT. 1,1970

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